Thromboxanes and prostacyclins are highly vasoactive substances synthesized from essential fatty acids via a common prostaglandin endoperoxide precursor. Thromboxanes released for human platelets or from guinea pig lung during anaphylaxis stimulate platelet aggregation and induce contraction of rabbit aorta strips. The recently discovered prostacyclins synthesized by vascular endothelium have opposite effects, inhibiting aggregation and inducing relaxation of coronary arteries. The principal objective of this project is to investigate factors influencing the formation of prostacyclins and thromboxanes from 14C-arachidonic acid in platelets and vascular tissues in vitro. These studies will be supplemented with experiments using isolated endothelial, lung, heart, and smooth muscle cells maintained in tissue culture. Specific factors to be investigated will include the functional interrelationships between vascular endothelial cells, which are unable to synthesize the endoperoxide precursor, and platelets or underlying smooth muscle cells which can provide this. An aorta strip chamber model has been developed in which prostacyclin synthesis can be measured in normal aorta strips. The changes induced by physical de-endothelialization, trypsin treatment, atherosclerosis, or by puncture damage can then be studied. A number of anti-inflammatory and anti-platelet drugs, including aspirin, fenamic acids, and phenylbutazone and indomethacin, which have been shown to inhibit synthesis of prostaglandins, will be tested for their effects on thromboxane-prostacyclin synthesis in these experimental systems. These investigations should provide badly needed information on the biological role of the prostacyclins and thromboxanes in vascular tissues in vivo and the influence of anti-inflammatory-anti-platelet drug therapy on the dynamics of platelet-vasculature interactions.